1,2-butylene oxide is a colorless liquid, soluble in water and miscible with most organic solvents. It is commercially important as an intermediate for various polymers, including poly 1,2-butylene oxide. High molecular weight poly 1,2-butylene oxide (poly BO) can be used as a high efficiency viscosity index (VI) improver for both synthetic and non-synthetic oils. A viscosity index (VI) improver is a lubricating oil additive that has the effect of increasing the viscosity of the oil in such a way that it is greater at high temperature than at low temperature. The development of such a poly BO viscosity index improver is commercially important. Such development involves the efficient polymerization of 1,2-butylene oxide (BO) to a molecular weight high enough to give a good VI, while limited as to shear stability. BO does not polymerize to a high molecular weight as readily as ethylene oxide (EO) or propylene oxide (PO) due to steric reasons, but at the same time, its character is more hydrocarbon-like and oil compatible than either EO or PO. Currently, there is considerable emphasis being placed on the development of high molecular weight poly BO. Common catalysts like KOH/alcohol, i.e. alkoxides, are not stereospecific and fail to give high molecular weight poly BO. Use of other more sophisticated anionic techniques has also failed to give stereospecific high molecular weight polymer. Very high molecular weights have been obtained with magnesium-AcAc catalysts which have given outstanding VI, however, these samples of poly BO have been quite susceptible to shear degradation.
Coordination catalysts were proven to be most effective initiators for the preparation of high molecular weight poly BO. Such catalysts include zinc diethyl-water complexes, organo magnesium complexes, double metal cyanide complexes, and a complex formed with zinc xanthate, N-butanol and triethylaluminum. Even though the molecular weights have been high, the results have not been very attractive. Some of the coordination catalysts produced poly BO having an excessive molecular weight for practical applications evidenced by the fact it is readily degraded by shear. For the other coordination catalysts, the poly BO yield is low even through high molecular weight polymers are obtained. Polymerization of BO by ionic mechanisms is also known, but the products have been of low molecular weight.
U.S. Pat. No. 2,706,181 discloses that a partially hydrolyzed complex of propylene oxide (PO) and iron chloride (FeCl.sub.3) is an effective catalyst in the preparation of high molecular weight isotatic poly propylene oxide (PO). Low molecular weight poly PO was obtained as well. However, this catalyst does not work to polymerize BO, and an analogous catalyst for polymerizing BO and PO monomer has not been known because of difficulty in the process of obtaining a partially hydrolyzed product. Attempts to make an analogous catalyst to that of U.S. Pat. No. 2,706,181 for the preparation of poly BO employing iron chloride FeCl.sub.3 have failed because it has been impossible to produce a controlled and selective partial hydrolysis of the catalyst precursor. The effectiveness of this type catalyst depends largely on the success of the hydrolysis step in production.
Problems found in this partial hydrolysis step en route to a catalyst for prolymerizating BO are successfully overcome by the novel and unobvious method of the present invention. Thus, by this invention, it is now possible to prepare an iron chloride-BO-water catalyst for polymerizing BO easily.